Searching for a Fundamental Heating Mechanism in Low-Activity Dwarfs

M. Mathioudakis(1)

1) Center for EUV Astrophysics, 2150 Kittredge Street, University of California, Berkeley, CA 94720

To appear in Astrophysical Letters and Communications, presented June 1995 at the NATO ASI on Solar and Stellar MHD Flows in Crete, Greece.

Abstract

The detection of a well-defined lower limit in the surface flux versus color diagrams, and the fact that all late-type dwarfs examined have chromospheric Mg II emission cores, shows that the formation of chromospheres in late-type dwarfs is universal. This result implies that a basic, fundamental heating mechanism exists in the atmosphere of late-type dwarfs. Recent results in the extreme ultraviolet and in X-rays have shown that low-activity dwarfs have detectable coronal emission. Their corona is characterized by relatively cool temperatures, typically less than a few million degrees. Current theories of acoustic heating reproduce quite well the observational parameters of low-activity dwarfs. However, the basal emission could also arise from a fundamental magnetic rather than acoustic heating mechanism. We review the observational properties of low-activity dwarfs and compare them with current theories of atmospheric heating.

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